Commercially available high purity tin is generally produced by an electrolytic method using an acidic tin solution such as tin sulfamate, tin sulfate, tin chloride or the like.
For example, Japanese Patent Application Laid-open Publication No. S62-1478 B (Patent Literature 1) describes a method for carrying out electrolysis in an electrolytic bath having a liquid composition containing 30 to 150 g/L of Sn and 30 to 200 g/L of sulfamic acid that contains few radioisotope elements, using 99 to 95% by weight or more of tin as an anode, under electrolytic conditions of a cathode current density of 0.5 to 2.0 Amp/dm2 and a liquid temperature of 15 to 50° C., for the purpose of lowering a emission (claim 2 of Patent Literature 1).
Japanese Patent No. 2754030 B1 (Patent Literature 2) describes a method for producing tin characterized in carrying out electrolysis in an electrolytic solution containing 90 to 240 g/L of sulfuric acid that at least conforms to the standard of the first class grade sulfuric acid defined in JIS K 8951 and 10 to 50 g/L of hydrochloric acid that at least conforms to the standard of the first class grade hydrochloric acid defined in JIS K 8180 using tin having a purity of 99.97% by weight or more as an anode, for the purpose of lowering a emission (claim 1 of Patent Literature 2).
Japanese Patent 3882608 B1 (Patent Literature 3) describes a method for removing lead by electrolytic refining of impurities in metallic tin. More particularly, it describes a method of electrolytic refining of high purity tin using an electrolytic solution made from a mixed acid of sulfuric acid and silicofluoric acid, which includes withdrawing the tin electrolytic solution from an electrolytic bath and routing it to a precipitation tank; adding strontium carbonate to the electrolytic solution in the precipitation tank to precipitate lead in the solution at a liquid temperature of 35° C. or lower; then routing the electrolytic solution containing said precipitates to a filter unit to separate the precipitates by filtration; and recycling the precipitates-removed electrolytic solution to the electrolytic bath and carrying out electrolytic refining of tin (claim 1 of Patent Literature 3).
Japanese Patent No. 5296269 B1 (Patent Literature 4) discloses a method for conducting electrolytic refining by leaching tin as a raw material with an acid such as sulfuric acid to form a leached solution as an electrolytic solution, suspending an adsorbent for impurities in the electrolytic solution, conducting the electrolytic refining using a raw material Sn anode, thereby obtaining high purity tin having a purity of 5 N or more (excluding gas components of O, C, N, H, S and P). More particularly, it describes a method for conducing electrolytic refining in a sulfuric acid bath or a hydrochloric acid bath using tin having 3 N level as the anode at an electrolysis temperature of 10 to 80° C. and under a condition of a current density of 0.1 to 50 A/dm2. It also discloses that impurities are adsorbed by suspending an oxide such as titanium oxide, aluminum oxide and tin oxide, as well as activated carbon, and carbon in the electrolytic solution.
On the other hand, non-Patent Literature 1 discloses that tin is used as a raw material of a tin droplet target used for generating an EUV (Extreme Ultraviolet) light source for lithography.